1. Field of the Invention
The present invention relates to a vibrator and, more particularly, to a vibrator used in a vibratory gyroscope that is applied to a navigation system which detects a position of a mobile by detecting its angular velocity and properly guides it, or to a yaw rate sensor which detects external vibration for the purpose of properly damping it.
2. Description of the Prior Art
FIG. 8 is a perspective view showing an example of a conventional vibrator for a vibratory gyroscope, and FIG. 9 is a sectional view taken along the line IX--IX of FIG. 8. The vibrator 1 comprises a vibrating body 2. The vibrating body 2 is formed into a regular triangular prism shape with, for example, a constant elastic metal material. On centers of three side faces of the vibrating body 2, piezoelectric elements 3a, 3b and 3c are bonded, respectively. The piezoelectric elements 3a, 3b and 3c are made, for example, by forming electrodes on both surface of a piezoelectric ceramic, respectively.
In the vibrator 1, for example, two piezoelectric elements 3a and 3b are used for driving and for detecting, the other piezoelectric element 3c is used for feedback.
Furthermore, in the vibrator 1, since the vibrating body 2 is formed into a regular triangular prism shape; a resonance frequency on driving side coincides with a resonance frequency on detecting side.
When the vibrator 1 is used in a vibratory gyroscope, for example, between the piezoelectric element 3c for feedback and the piezoelectric elements 3a and 3b for driving, an oscillation circuit is connected as a feedback loop for self-driving. By a signal from the oscillation circuit, the vibrating body 2 bends and vibrates in a direction orthogonal to the face whereon the piezoelectric element 3c for feedback is formed. When the vibrator 1 is rotated in this state, a difference of output voltages is produced between two piezoelectric elements 3a and 3b for detecting, the rotational angular velocity can be detected by measuring the difference of the output voltages.
Meanwhile, in the vibrator 1, for example, two piezoelectric elements 3a and 3b can be used for feedback and detecting, the other piezoelectric element 3c can be used for driving.
In the vibratory gyroscope used the vibrator shown in FIG. 8 and FIG. 9, a circuit for processing an output signal is connected. The circuit includes an amplifier having a variable resistor, the sensitivity of the vibratory gyroscope is controlled by adjusting the variable resistor.
However, when such a circuit is used, the vibratory gyroscope becomes a large size, it can not meet the demands of small size and lightweight.
Also, in the vibrator shown in FIG. 8 and FIG. 9, since the resonance frequency on driving side coincides with the resonance frequency on detecting side, an equivalent quality factor on detecting side is high. Therefore, in the vibrator, a phase lag of an output on detecting side is large, the output response characteristic is bad.
Furthermore, in the vibrator shown in FIG. 8 and FIG. 9, since the resonance frequency on driving side coincides with the resonance frequency on detecting side, the oscillation frequency of the vibrator coincides with the resonance frequency on detecting side. However, since the impedance frequency characteristic of the vibrator is nonlinear around the resonance frequency, when the oscillation frequency or the impedance frequency characteristic of the vibrator is changed by temperature change, a drift component is easily generated in the output difference between two piezoelectric elements for detecting.